(1) Field of the Invention
This invention generally relates to an environmentally clean device to eliminate or destroy unwanted underwater objects remotely without using explosive materials. More particularly, the invention uses a general-purpose active sonar array to remotely eliminate or destroy unwanted underwater objects.
(2) Description of the Prior Art
The current art for the underwater destruction of unwanted objects is as varied as the devices to be destroyed.
The following patents, for example, disclose a generating a cavitation area at a very close range and/or within an enclosed space and at high frequencies, but do not disclose generating a cavitation in an essentially free water space and at relatively low frequencies in order to destroy a target within that free space.                U.S. Pat. No. 4,244,749 to Sachs et al.;        U.S. Pat. No. 4,681,264 to Johnson, Jr.        U.S. Pat. No. 5,035,363 to Somoza;        U.S. Pat. No. 5,209,221 to Reidlinger;        U.S. Pat. No. 5,681,396 to Madanshetty; and        U.S. Pat. No. 5,827,204 to Grandia et al.        
Specifically, Sachs et al. discloses removal of biofouling from the external surfaces of spaced apart pipes of a heat exchanger which are in contact with a liquid by positioning a plurality of ultrasonic transducers between the pipes and operating the transducers at sufficient power levels to cause cavitation within the liquid to effect the desired cleaning action. The transducers are arranged in a planar configuration to produce bi-directional acoustic radiation. Various types of instrumentation are provided for determining the extent of biofouling and effectiveness of cleaning as well as for monitoring transducer operation parameters.
The patent to Johnson, Jr. discloses a process and apparatus for enhancing the erosive intensity of a high velocity liquid jet when the jet is impacted against a surface for cutting, cleaning, drilling or otherwise acting on the surface. A preferred method comprises the steps of forming a high velocity liquid jet, oscillating the velocity of the jet at a preferred Strouhal number, and impinging the pulsed jet against a solid surface to be eroded. Typically the liquid jet is pulsed by oscillating the velocity of the jet mechanically or by hydrodynamic and acoustic interactions. The invention may be applied to enhance cavitation erosion in a cavitating liquid jet, or to modulate the velocity of a liquid jet exiting in a gas, causing it to form into discrete slugs, thereby producing an intermittent percussive effect.
Somoza discloses reducing the particle size of energetic explosive materials by slurrying the particulate explosive materials in an inert liquid such as water or an aqueous solution, and subjecting the slurry to intense acoustic cavitation from an ultrasonic generator for a short time. The particulate explosive materials are rapidly ground to a small particle size while minimizing the danger of detonation.
Riedlinger discloses a device for generating sonic signal forms for limiting, preventing or regressing the growth of pathological tissue that comprises an ultrasonic transmission system for transmitting sound waves, focused on the tissue to be treated, by way of a coupling medium. An ultrasonic signal produced at the focus of the system comprises brief pulses having at least one rarefaction phase with a negative sonic pressure amplitude with a value greater than 2×105 Pa. The ultrasonic signal is radiated with a carrier frequency exceeding 20 kHz, a sonic pulse duration T of less than 100 μs and a pulse recurrence rate of less than 0/(5T). The device produces controlled cavitation in the tissue to be treated.
The patent to Madanshetty discloses the surgical cleaning of a semiconductor wafer through the inducement of cavitation on the surface of the wafer at the location of an adherent particle. Cavitation is induced by focusing two acoustic fields on the surface of the wafer. The two acoustic fields include a cavitation field having relatively low frequency focused on the wafer surface from a direction perpendicular to the wafer and a coaxing field of relatively high frequency focused on the wafer surface from a direction between 0 and 25 degrees from the wafer surface.
Grandia et al. discloses medical noninvasive operations using focused modulated high power ultrasound that generally includes a transmitter for exciting a multifrequency ultrasound wave for causing vaporous cavitation bubbles in a small focal zone of a medical target region. Focused ultrasound can be used for both dissolving tissues as well as causing clots in order to destroy cancerous growths. The multifrequency wave includes an underlying low frequency signal for enabling optimal growth of microbubbles and at least one high frequency signal for enabling a narrow zone of focus of the ultrasound. A cavitation monitor may be provided for sensing a level of cavitation as well as providing feedback to the transmitter. In addition, an imaging system is provided for enabling viewing of the medical target area during the therapy.
It should be understood that the present invention would in fact enhance the functionality of the above patents by providing an array of intersecting acoustic beams in free water space, the acoustic beams being generated at a frequency and range to create a destructive cavitation field around an undesirable remote target.